Eye tracking devices for determining where a person is looking at a given time are well known in the art. Such devices typically include a first video camera for capturing a scene and a second video camera for capturing eye movement of the person. The video streams are processed to produce a single video, which shows the scene and includes a pointer that identifies where the person is looking at any given time.
In general, eye tracking devices are calibrated prior to use in order to establish a mapping between the eye coordinates as they appear in the second video camera image and the scene image. Often, re-calibration is required when changes in environmental circumstances, such as ambient light levels, for example, occur.
Eye tracking devices that are worn as accessories by the person, such as eye glasses or helmets, for example, often slip, get bumped or are removed. All of these actions reduce the accuracy of an eye tracking device because the mapping between the eye camera and scene camera generally becomes less accurate as a worn accessory is moved from its originally calibrated location.
The calibration process is time consuming and requires a directed effort by the person. It is therefore desirable to provide a method and apparatus for maintaining calibration of an eye tracking apparatus.